New Treatment for Mare Endometritis Examined (AAEP 2011)

We'd all like to think that a mare's womb is a warm, dark, nurturing environment perfect for transforming a small fertilized egg into a healthy foal in 340 days. According to equine reproductive specialists, however, uteri can be lined with bacterial "biofilm" containing millions of antibiotic-resistant bacteria in a glutinous, jellylike substance that in some cases can prevent mares from conceiving, much less carrying a foal to term.

One of these specialists presented an alternative to traditional antibiotics for treating endometritis--or inflammation of the uterine lining--at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas. Endometritis can occur post- breeding in reproductively normal mares or those with structural abnormalities of their reproductive tracts that allow bacteria to enter the uterus. In either case endometritis is an important cause of infertility in mares. Veterinarians usually treat it with antibiotics and by flushing the uterus, but in some mares this approach may not be sufficient to resolve the inflammation.

"The bacteria in the biofilm can be up to 500 times more resistant to antibiotics than the same type of bacteria grown in cultures in a lab, and many are also resistant to common antibiotics used in practice. Equine veterinarians therefore need to consider the use of 'alternative' methods to treat endometritis in mares rather than relying solely on traditional antibiotics to improve pregnancy rates and treat infertility," said Sara Lyle, DVM, PhD, Dipl. ACT, assistant professor of theriogenology in the Department of Veterinary Clinical Sciences at Louisiana State University's School of Veterinary Medicine.

She explained that one adjunctive therapy for treating endometritis is to wash the uterus with a special "solution" called a buffered chelating agent.

"A third-generation buffered chelating agent either with or without antibiotics removes ions from the cell walls of bacteria, reducing the integrity of the cell wall," Lyle explained. "The exudate produced by the disrupted bacteria and biofilm is subsequently removed and the mare can be bred."

Veterinarians can prepare buffered chelators in-house using standard laboratory equipment, or they are commercially available with and without traditional antibiotics.

Lyle and colleagues tested this buffered chelator in eight reproductively normal mares and eight mares with known fertility problems. Their key findings were:

In normal mares the researchers noted no adverse effects, and the buffered solution did not have any deleterious effects on the endometrium or the establishment of pregnancy;

A buffered chelator solution might be useful in clinical cases of chronic endometritis due to the presence of either Gram-negative bacteria or even fungi; and

Six of the eight mares with reproductive issues became pregnant and foaled following treatment. The other two became pregnant but experienced early embryonic loss.

Lyle warned, "Treatment failures may still occur if concurrent anatomic abnormalities in the mare's reproductive tract exist, such as an incompetent cervix, which supports the recurrence of endometritis."

Nonetheless, according to the Lyle et al., "The increasing frequency with which antibiotic-resistant bacteria are being recovered from the equine uterus is concerning, and treatments that can reduce our dependence on traditional antibiotics alone are worthy of consideration."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.